The present invention relates to transit concrete mixers More particularly, the present invention relates to a stretch trailer which carries a concrete mixing drum and related discharge equipment.
Transit concrete mixing trucks usually have a unitary frame which carries a cab and a rotatable drum behind the cab. The drum contains and mixes the concrete during transport. Such trucks further typically include steerable wheels beneath the cab and rear drive wheels in a dual axle arrangement. For additional support when the mixing drum is full, such trucks may also be equipped with one or more auxiliary wheel assemblies. Such auxiliary wheel assemblies can typically be pivoted between a ground engaging, load bearing position when the mixer is full and moving along public highways and an elevated, stowed position when the truck is empty or traveling off-road.
The typical arrangement described above, however, suffers from limited capability both from a maneuverability standpoint and because of governmental restrictions. For example, highway weight restriction laws allow a gross weight of 80,000 pounds on five axles provided that the front and rear axles are spaced by at least fifty feet, seven inches. At the same time, most states limit the length of trucks having a unitary frame to only forty feet. Thus, the only way to achieve the axle spacing need to carry the maximum load is the utilize a tractor-trailer arrangement.
Use of a typical tractor-trailer arrangement creates its own problems. For example, if a mixing drum is properly mounted on a standard trailer frame, to achieve proper balance, the discharge chute of the mixing drum should be mounted over the rear wheels in a position which tends to make access to the chute very awkward. More specifically, the wheels interfere with proper discharge of the concrete from the drum. If the drum is mounted on a typical trailer frame in a position to avoid this problem, proper balance is lost.
It is therefore an object of the present invention to provide a transit concrete mixer which is capable of legally achieving a 50'-7" span and a gross weight of 80,000 pounds.
Another object of the present invention is to provide such a concrete transit mixer so that the wheels and frame do not interfere with discharge of the concrete.
Still another object of the invention is to provide such a mixer which has a low center of gravity when the unit is loaded and traveling down the road.
A further object of the present invention is to provide such a concrete transit mixer which has a high ground clearance when the vehicle is driven off-road.
Another object of the invention is to provide a transit mixer which has an elevated rear end to allow the discharge mechanism to be at a greater height.
Still another object of the invention is to provide a transit mixer with means for reducing the length of the trailer frame when necessary for maneuverability or to place added weight on the drive wheels of the tractor for greater traction.